The long-term goal of this work is to understand the structural and functional changes imposed on the central auditory system by conductive hearing impairment. A secondary goal is to determine the factors that govern the potential for reversibility of these changes. The clinical implications of this work are that many children experience conductive hearing loss during early development, in a time period that coincides with that of rapid acquisition of speech and language skills. Childhood conductive hearing loss is known to be associated with deficits in auditory processing skills, some of which persist even after the return of normal hearing. The nature of the functional and neuroanatomical changes in the central auditory system that underlie these deficits is unknown. The hypothesis underlying this proposal is that chronic conductive hearing impairment in early life results in structural changes in the central auditory systems, which are related to functional deficits in central auditory processing. These effects are age-dependent, and more severe in the developing animal. The severity of the structural change will affect the potential for reversibility when normal hearing is reinstated. Experiments are proposed to achieve three specific aims designed to address this hypothesis: 1) to define the effects of conductive hearing loss on activity in the auditory nerve and central auditory system, and assess the agedependent interactions; 2) to define the metabolic and structural changes that occur following unilateral conductive hearing loss in the developing and mature animal; and 3) to investigate factors that govern the reversibility of the above changes. We hypothesize that the potential for reversibility will depend upon the type and severity of the structural modification induced by conductive impairment, and the developmental stage of the animal at the time of the insult.